The author suggests two methods:

• e-mail;
• Annotate the online book.

For comments that are closely related to the text of the book and, in particular, for reporting errors, the annotation method is recommended. Just head to the online book and click the icons in the top right corner, or select some text (annotation icons will pop up). You will need a free account on Hypothes.is. Terms and conditions related to the annotations are those set by that organization, not the author of this book. Please consider this facility experimental for the time being.